The present invention relates to data acquisition devices. More particularly, the invention relates to an environmentally sealed data acquisition device with an internal activation circuit.
Many sensors and other data acquisition devices are intended for outdoor use or in other harsh environments and therefore must be hermetically or environmentally sealed to prevent unwanted entry of water and other contaminants. Ideally, these devices should contain no external on/off switches or other components that could provide a pathway for contaminants. Unfortunately, the lack of an external on/off switch prevents easy activation of the devices once they are ready to be used.
Passive radio frequency identification (RFID) devices solve this problem by powering their internal circuits with current induced by an external interrogation device. Although this eliminates the need for an external on-off switch and an internal battery, these devices are not useful for applications requiring remote and/or longer-lasting sensing because they only remain activated while in the presence of an interrogation signal. Moreover, these devices typically have very short interrogation and transmission ranges, further limiting their use in applications requiring remote sensing.
Active RFID devices are sometimes preferred over passive RFID devices because they include their own internal batteries and therefore can acquire data without the constant presence of an external interrogation signal. Unfortunately, however, active RFID devices either require an external on/off switch to activate their batteries, which makes them difficult to seal as described above, or include circuits that are constantly on, resulting in premature battery discharge.
Turn-on circuits for active RFID devices have been proposed to solve some of the above-described problems, but such turn-on circuits still require the constant presence of an external interrogation signal. Once the external interrogation signal is removed, the internal circuits of these devices are turned off, thus limiting their use in applications requiring remote and longer-lasting sensing.